The immune system serves a vital role in protecting the body against infectious agents. It is well established, however, that a number of disease states and/or disorders are a result of either abnormal or undesirable activation of immune responses. Common examples include graft versus host disease (GVHD), organ or graft rejection, inflammation, and autoimmune linked diseases such as multiple sclerosis (MS), systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA).
In general, an immune response is activated as a result of either tissue injury or infection. Both cases involve the recruitment and activation of a number of immune system effector cells (i.e. B- and T-lymphocytes, macrophages, eosinophils, neutrophils, etc.) in a process coordinated through a series of complex cell-cell interactions. A typical scenario by which an immune response is mounted against a foreign protein is as follows: Foreign proteins captured by antigen presenting cells (APC's) such as macrophages or dendritic cells are processed and displayed on the cell surface of the APC. Circulating T-helper cells (TH cells), which express an immunoglobulin that recognizes (i.e. binds) the displayed antigen undergo activation by the APC. The activated TH cells in turn activate appropriate B-cell clones to proliferate and differentiate into plasma cells which then produce and secrete humoral antibodies targeted against the foreign antigen. The secreted antibodies bind to any cells expressing the foreign protein, targeting such cells for destruction by other immune effector cells.
When TH cells contact B cells this stimulates B cell proliferation and immunoglobulin (Ig) class switching from IgM to IgG, IgA or IgE classes. Various receptor-ligand interactions are involved in mediating contact between a TH cell and a B cell during the response to a T-dependent antigen. In particular, CD40—CD40 ligand (CD40L) pairing is critical to achieving this cell-cell interaction. CD40L is not expressed on resting TH cells but is induced after the cell contacts T-dependent antigen. The B cell is stimulated by CD40L through the CD40 antigen on the B-cell surface and, in combination with IL-4, mediates the secretion of IgE.
CD40L and CD40 are both transmembrane glycoproteins within the family of tumor necrosis factor (TNF) and TNF receptors, (TNF-R), respectively. Human CD40 is a peptide of 277 amino acids having a molecular weight of 30,600, a 19 amino acid secretory signal peptide comprising predominantly hydrophobic amino acids and cysteine-rich motifs in the extracellular region. The protein contains a putative leader sequence, transmembrane domain and a number of other features common to membrane-bound receptor proteins.
Human CD40L is a type II membrane-bound glycoprotein (Spriggs et al., J. Exp. Med. 176:1543 (1992)). Murine CD40L has also been cloned (Armitage et al., Nature 357:80 (1992)). CD40L has an extracellular region at its C-terminus, a transmembrane region and an intracellular region at its N-terminus. Soluble CD40L comprises an extracellular region of CD40L (amino acid 47 to amino acid 261). CD40L induces B-cell proliferation in the absence of any co-stimulus, and can also induce production of immunoglobulins in the presence of cytokines. CD40L activity is mediated by binding of the extracellular region of CD40L with CD40.
CD40 is expressed on B lymphocytes and participates in many B cell functions in addition to inducing Ig class-switching, such as acting as a cofactor with specific antigen and certain lymphokines for B cell mitogenesis, preventing apoptotic cell death and triggering B cell adhesion to other cells. CD40 is also expressed on cell types other than B-cells, including macrophages, dendritic cells, thymic epithelial cells, Langerhans cells, and endothelial cells. These findings have led to the current belief that CD40 plays a broad role in immune regulation by mediating interactions of T-cells with B-cells as well as with other cell types. In support of this notion, stimulation of CD40 in macrophages and dendritic cells is required for T-cell activation during antigen presentation (Gruss et al., Leuk. Lymphoma, 24:393 (1997)).
Evidence indicates that CD40 participates in tissue inflammation as well. Production of the inflammatory mediators IL-12 and nitric oxide by macrophages have been shown to be CD40 dependent (Buhlmann and Noelle, J. Clin. Inmunol. 16:83 (1996)). In endothelial cells, stimulation of CD40 by CD40L has been found to induce surface expression of E-selectin, ICAM-1, and VCAM-1, promoting adhesion of leukocytes to sites of inflammation (Buhlmann and Noelle, J. Clin. Immunol., 16:83 (1996); Gruss et al., Leuk. Lymphoma, 24:393 (1997)). Finally, studies of CD40 overexpression in epithelial and hematopoietic tumors as well as tumor infiltrating endothelial cells indicate that CD40 may play a role in tumor growth and/or angiogenesis (Gruss et al., Leuk. Lymphoma, 24:393 (1997); Kluth et al., Cancer Res., 57:891 (1997)).
Due to the role that CD40 plays in humoral immunity therapeutic strategies aimed at modulating CD40 can be useful in treating a number of immune associated disorders. For example, inhibition of CD40 activity could reduce graft-versus-host disease (GVHD), graft rejection, and autoimmune diseases such as multiple sclerosis (MS), systemic lupus erythematosus (SLE), and certain types of arthritis. CD40 inhibitors may also be useful as an anti-inflammatory compound, and could therefore be useful in treating a variety of inflammatory and allergic conditions such as asthma, rheumatoid arthritis, allograft rejections, inflammatory bowel disease, various dermatological conditions, and psoriasis. Inhibitors of CD40 may be useful as anti-tumor agents and inhibitors of other hyperproliferative conditions as well.
Promoters or stimulators of CD40 activity may be useful for increasing humoral immunity to resist an infectious agent, such as a viral or bacterial pathogen. Promoters may also be useful in stimulating or potentiating humoral immunity against tumors. In addition, promoters or stimulators of CD40 activity may be useful in promoting memory thereby improving the rapidity or robustness of the immune response.
Monoclonal antibodies directed against either CD40 or CD40L in animal models indicate that inhibition of CD40 stimulation would have therapeutic benefit for GVHD, allograft rejection, rheumatoid arthritis, SLE, MS, and B-cell lymphoma (Buhlmann and Noelle, J. Clin. Immunol, 16:83 (1996)). Antibodies to CD40 therefore have the potential to be highly effective therapeutic agents—antagonistic anti-CD40 antibodies can be used as immunosuppressive/anti-inflammatories, while agonistic anti-CD40 antibodies can be used as immunostimulants to boost immune responses in, for example, individuals with compromised immune systems. Several anti-CD40 antibodies are currently in development which are murine, chimeric or humanized. However, non-human or humanized antibodies are limited in their effectiveness because of the development of immune responses to the non-human portions. The invention addresses this problem and provides related advantages.